dingy

SDB, What experience do you have with MK II's ??
Tis alot different to the scoob.
Any Help is good..

Narrow wheels for traction.....er gonna go wider actually, Monte Carlo Style....

Davvers

JFS that was me in the R500 - we had fun didn't we, must say thats the only trackday I've been to where any car has been up my chuff. Agree with you completely - I always cocked up school - the long right hander after the straight - and the westie had more grunt down the straights - however the R500 better through the more technical abotts/Radar/Mountfield complexes.
Excuses? CR500s aren't as good as ACB10s - I know use slicks much better!! Also it was my first trackday with that car - still a bit new to me, have done a 46.5 since then F3 record is 44.9 so not too bad.

FANCY A REMATCH???
LOL!

DavidBrown

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by dingy:
<B>SDB, What experience do you have with MK II's ??[/quote]

I'd have thought the principles of suspension dynamics are pretty universal ?

SDB

dingy

I've rallied a couple, tested maybe 5, and completed 1000's of miles of demo driving in others. Admitedly, these were all competition cars.

My experience with Scoobs is limited to only the last 3 years.

Principles of suspension and chassis dynamics are uniform, there are just slightly different ways of applying them to different cars with different suspension layouts.

Wider tyres will almost definitely reduce longitudinal grip (accelerating / braking) unless you can run them at lower pressures.

The reason for this is that the contact patch becomes shorter (although wider) and it is the length of the contact patch which most affects the longitudinal grip (and the width, the lateral grip). So you should end up with more (in theory) cornering grip, but less traction. It's a very common mis-conception.

Cheers

Simon

dingy

Yeah they are mate, just wondered if he had worked on a MK II before...

SDB

ooh..

thought of another one.. (lol)

- reduce rear camber (towards zero)

SDB

actually scratch that... as I don't know what the dynamic camber is doing, so that could be really bad advice. apologies

dingy

Rear camber is fixed at Zero mate. Tis a fixed Axle.

If you Drove them, did you help set them up..

IE regarding front negative camper etc.

SDB

Hi Dingy

(what a muppet re: rear camber. sorry! )

I just did the test driving on the ones I tested, so I don't know the technical intricacies or anything like that.

But.. as I said, I can help with the set-up as the low level principles are the same no matter what car you're working on.

for instance.. you mention front camber...

Camber is set to try to get the contact patch as square on the road as possible during cornering (and particularly turn-in for the fronts) and also (this one is not as obvious) to utilise the benefits of camber thrust (the lateral force that pushes in the direction of the camber)...

but... negatives are :-

- inside camber goes *away* from optimal rather than towards it during cornering.
- reduced traction (braking, in the case of the fronts on a RWD car)
- reduced straight line stability
- darting handling due to camber thrust

there are also some little known positives like, wet grip *can* be increased in deep water due to the tyre cutting into the standing water.

Static camber is a necessary evil sometimes, but if you have full control over the suspension, in some situations it is better to increase castor, as that basically means that the -ve camber increases as you turn the wheel (which is when you want it most).

These are all standard throughout any type of car. So it is this kind of thing I was offering. People often make the mistake of saying things like "The MKII escort is said to be awesome with 1deg -ve camber." but that does not take into account every other aspect of the set-up (each aspect of which will affect the ideal -ve camber).

Cheers

Simon

SDB

Arron

You dissapoint me.

First of all..
Gravel is a TOTALLY different concept as you not only have the mechanical and chemical locking of the contact patch, but the equal and oposite reaction of the stones you throw backwards as the tyre spins.

Secondly

Tarmac..
Traction is not the only thing you need to win a rally you muppet! You need to go round corners as well.

If it was a simple case of wider tyre = more traction AND lateral grip, you would just stick 400mm wide tyres on the car and be done with it!!

In general terms, all other things being equal, making the tyre wider does the following main things...

1) Increases unsprung weight = bad
2) Widens the contact patch
3) Shortens the contact patch
4) Makes NO DIFFERENCE (roughly) to the contact patch area

The laws of the traction circle dictate that you cannot use all of the lateral grip AND all of the longitudinal grip at the same time.

Again, in general terms, the longer the contact patch (longitudinally) the longer the traction circle, and the wider the contact patch the wider the traction circle.

So the wider you make a tyre the more lateral grip it gives you (on dry tarmac), but the less longitudinal traction it gives you.

I look forward to you demonstrating your indepth knowledge of the subject with your explanation of why a wider tyre produces more traction.

Regards

Simon

[This message has been edited by Simon de Banke (edited 12 July 2001).]

SDB

PS. I was just trying to help

ARRON BIRD

Simon next time I watch race cars on dry or wet tarmac I must look for those weedy tyres you keep referring to. I`m sorry mate but I think your getting too techy again.
On gravel you will find works rally cars still using at least 205 width tyres and on four wheel drive cars such as the Subaru`s etc i`ve known 225`s to be used dependant on conditions.
In snow and ice we use to use tyres as narrow as165 with no spikes as they cut thro the ice better with a smaller contact patch.
Me I`ll always opt for the widest tyres I can fit under the arches on any car I`m competing in.
Even on wet Welsh stages we used to use 175 or 185 Dunlops and later we helped to develop the Yokohama tyres you see the works boys using now.
Mind you thats probably all bollox innit cos i must keep reminding myself I know fack all
Anyway cant wait to pass you on your 2CV tyres next time.
Maybe thats how you manage to do such good power slides hey
PS why is my new M3 coming with 255`s on the back and 225`s on the front when 165`s would do the job???

SDB

Arron

did you actually read my post?

*YOU NEED A WIDER TYRE IF YOU WANT TO PRODUCE MORE LATERAL GRIP*

I am not talking about running on skinny tyres..

If you ran on 2CV tyres, you would not be able to corner as fast as on wider tyres, and as you and I know, cornering is what wins rallies.

Dingy was saying he wanted more traction...

I simply offered a set-up change that will increase traction.. and I also mentioned that it would reduce cornering ability at the same time.

Arron... being able to drive (which I'm sure you can) is not the same as understanding what's actually going on. Nobody (especially me) is doubting the merit of your driving experience and probably competence, but you need to accept that you don't actually understand what's going on a lot of the time (same as all of us).

I am telling you from a standpoint of knowledge and experience, that what I have said is accurate.

Just because you didn't know that, doesn't mean that it isn't correct!

Regards

Simon

SDB

PS. I know you're going to argue with me on this, but again, I am telling you this because I KNOW it to be the case, not just assume.

The reason *most* performance cars are released with wider rubber is often purely asthetics! I know that sounds ridiculous, but often the tyre sizes that have been selected through testing that I've been involved in on road cars have been widened by the marketting department, against the wishes of the chassis dynamics team.

ARRON BIRD

I`m sorry Simon but when I`m flat out I dont have time to calculate my laterel from me longitudail????
Grip is grip
Most circuit cars dont go sideways as thats the slowest route as I`m sure youre aware.
Rallying is a different thing altogether again I`m sure you will agree.
Dingbat is looking for more traction around a circuit and in my book he wants GP4 tarmac spec for that.
I seem to remember (cos Im that old) that all the circuit MK2`s ran BIG arches and tyres when using big power engines or am I dreaming??
I can remember the MASS powered box arched MK2 using **** off big tyres.

W9GTR

Simon
Don't take this the wrong way but I'm not sure how u reach the conclusion that a wider tyre reduces the longitudinal contact patch.
I would naturally assume that the diameter of the wheel would directly affect this more than the width. I am however more than prepared to be enlightened by your War & Peace rivaling reply
BTW What affects lateral or cornering grip more? Width of tyre on front or the rear? I only mention this as a lot of track cars ie. F1 etc. do tend to have wide tyres on the back and narrow on the front and as they are normally rear wheel drive one naturally assumes that this is to increase traction during acceleration! and if your reasoning is taken literally one might assume that perhaps old schuey & co might be better served with my grifter wheels on his rear axle.


Lots of love
Steve



[This message has been edited by W9GTR (edited 12 July 2001).]

GP

hmmm - I was initially a little sceptical of this too, but then remembered something interesting I noticed about top fuel dragsters - ever noticed how under power their tyres go all tall and skinny... I suspect that if wide tyres were the best thing for straightline traction then they'd put on something much more like a huge F1 tyre no ?

something I always try to remember when arguing because I might have a bee in my bonnet...a closed mouth gathers no feet

W9GTR

Wot size fott does yer mouth tek?

BTW not arguing just asking the question
Steve

SDB

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>I`m sorry Simon but when I`m flat out I dont have time to calculate my laterel from me longitudail????[/quote]

you'd make a crap test driver then! And you would be surprised. If you are anything more than a complete moron when it comes to driving, you will be calculating you longitudinal and lateral grip ALL the way through the bend. If you are not.. you physically CANNOT be on the limit.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
Grip is grip
[/quote]

If you truly believe that, I can see why you are arguing.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>Most circuit cars dont go sideways as thats the slowest route as I`m sure youre aware.[/quote]

depends how you define "sideways". The actual fastest way around a corner is the angle at which all four tyres are at their optimal slip angle. This means there must be SOME slip on the back as well. If not, you could be going faster. But on the whole.. I agree.. big powerslide sideways action is just slow on a smooth circuit.

[qoute]<B>Dingbat is looking for more traction around a circuit and in my book he wants GP4 tarmac spec for that.</B>[/quote]

First of all, dingy only mentioned he wanted to "get the power down", so it had NOTHING to do with lateral grip.

Secondly, GP4 tarmac spec would be way off of the ideal for a smooth race circuit. Have you EVER done a tarmac rally with a surface even half way close to the likes of donnington??

Also, on a rally, the ability to change direction is priorities over ultimate cornering performance, so there would be a world of set-up changes required.

What you would really want is a race set-up, but I know nothing about racing so don't know what class to look at.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
I seem to remember (cos Im that old) that all the circuit MK2`s ran BIG arches and tyres when using big power engines or am I dreaming??
I can remember the MASS powered box arched MK2 using **** off big tyres.[/quote]

Mate.. you're making a muppet of yourself. I COMPLETELY AGREE that wide tyres are great! But I was just commenting that longitudinal traction is increased with a narrower tyre (at the expense of lateral grip).

If you have any useful information which shows why narrower tyres reduce longitudinal traction, could you post it. Otherwise, please don't tell me that something I *KNOW* to be true is rubbish just because your mate dave used to run 5000mm rears.

Cheers

Simon

jon hill

don't you also have to consider pressures ?

at extremes, a flat tyre has a huge contact patch and a solid concrete cement mixer wheel has a tiny contact point. I assume, thats why a wider tyre has lower longtitudinal grip - same amount of weight spread over a bigger area.

jon

SDB

W9

GREAT questions... (thank god!!)

OK..

front and rear makes no difference, it would just alter the grip at that end of the car.

jon is dead right.. the thing that affects the *AREA* of the contact patch is the load on it and the pressure..

the formula is roughly load / tyre pressue.

So the higher the pressure, the smaller the contact patch, and the loarger the load, the larger the contact patch.

The reason for the wider tyres on F1... (there is a lot more to it than this, but it's a good question so I'll give you the broad strokes).

F1 rears run at INCREDIBLY low pressures. This is to increase the area of the contact patch.

This also enables them to run wide tyres whilst not reducing the length of the contact patch.

The way to get more rubber on the road is to reduce the tyre pressures...

but if you did that to a narrow tyre, you would soon end up running on the actual rims. So a wider tyre allows you to run lower pressures.

BTW - while I'm here... having more rubber on the road DOESN'T (birdy will love this one) actually give you any more grip. The amount of grip you have is a function of the weight they tyre and the co-efficient of friction of the road / tyre interface. (this is not an exact science, as mechanical locking works differently to chemical locking)

What getting more rubber on the road DOES do, is spread the load across a wider aream so you reduce heat build up and wear.

Cheers

Simon

ARRON BIRD

Simon we are never going to agree again!
I`m soory but I think your theory is utter tosh!
GRIP IS GRIP sideways backways or whatever.
If whilst driving on the limit you have time to analyse all these diffring grips you mention your probably not trying hard enough.
Whilst I spent 2 years racing at National level with the likes of ex British Champion Andrew O`Hara I never once thought about putting narrow tyres on my kart unless it was wet and only then were the rear tyres about the same width as the rears and tyre pressures considerably higher.
In the dry the rear tyres were a quite a bit wider and if it was a hot day running as little as 10psi with bead retainers on the wheels to stop the tyres peeling off the rims.
A tyre is a tyre and whatever shape or size it is it will react in the same way o heat and conditions etc.
On track on bikes we run less pressure in the rear tyre than we do the front as greater heat is generated at the read DRIVEN wheel.
Even tho a bike tyre spends a lot of its time on the side it still doesnt affect the heat etc.
Mind you on a circuit which has mainly RH corneers the LH side of the tyre is usually colder so you do have to be a bit carefull.
Any how I`m bored now so I look forward to your informative and engineeringly perfect response.
Try to bring into it a little G force aswell eh

[This message has been edited by ARRON BIRD (edited 12 July 2001).]

W9GTR

Simon
AAAAAAhhhhh I see so in fact what u are telling me and dingy is my lardy arsed (your words not mine) coupe might just be in with a shout of producing more lateral grip than than his skip because it weighs more and has wider tyres
The baits out and I'm a waitin
Cheers
Steve
BTW refreshingly brief reply for U Simon

SDB

Arron

Everyone reading this thread can see how ridiculous your constant remarks to "I run wide tyres" are to the argument of what produces longitudinal traction.

I am sure that everyone apart from you can also see that I have already said "many times" that wide tyres are indeed better in most cases, so I am not advocating narrow tyres.

I am NOT going to explain that I was only saying *X,Y,Z* again, as it's in every post I've made.

I can tell you now Birdy. And whether you believe this or not, I'm affraid it is WITHOUT QUESTION a fact. On the subject of tyres, you have no idea what you're talking about.

But please write a book about your indepth knowledge and maybe the chassis and suspension engineers at Ford, Daimler Chrysler, Jaguar, and countless motorsport teams could learn how you have redefined the laws of physics and the entire concept of what makes a tyre work.

(deeply) dissapointed regards

Simon

SDB

LOL

W9.. again.. AWESOME question...

unfortunately it's not that simple...

When cornering the job of the tyres is to resist the lateral forces of the body mass.

In addition a tyre produces less *EXTRA* grip, the more weight you put on it...

so in other words, if you double the load on a tyre, it doesn't produce double the grip (although it does produce MORE grip).

So all other things being equal, you could simplify it by saying...

The heavier the car, the more mass there is to resist, and the lower *RELATIVE* friction there is to resist it.

Cheers

Simon

ARRON BIRD

Simon I am a racer.
I dont give a **** about all the stuff I`m reading I only know what I see being used to good effect.
I have no interest in the lateral whatever.
All I know is wider tyres are better in the context of this thread discounting all the other factors you quickly included.
I see NO performance car running narrower tyres and thats what this all started of as.
I have chosen not to have 19" rims on my M3 as I HAVE TESTED FULLY the ride and handling and grip levels on both 18`s and 19`s.
IF however the 19" wheels actually had wider tyres other than just a different profile the situation may be dofferent.
The handling is better on the 18`s
Now lets talk about pretty flowers and ***** cats.

[This message has been edited by ARRON BIRD (edited 12 July 2001).]

ARRON BIRD

Oh and also I dont remember reading in the early post anything about chassis set up.
It started of as you saying he`d be better of with narrow tyres.
Even tho his car handles like an upside down shopping trolley wider tyres are gonna help his cause because he`s only interested in Bars of PSI and power anyway.
Funny how I spent more money on getting my bike`s suspension and tyres sorted before any mods to the engine eh.
God I`m bored at work today.........does it show ?????

Blow Dog

Oi, leave the Evo's out of this.

SDB

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
All I know is wider tyres are better in the context of this thread discounting all the other factors you quickly included.
[/quote]

The context of the thread (or rather the post I was answering) was "getting the power down" = longitudinal traction.

You *don't* know that wider tyres are better for this, as it is not true.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
I see NO performance car running narrower tyres and thats what this all started of as.
[/quote]

Narrower than what? They run narrower tyres than if they'd put wider ones on!!! why haven't they put wider tyres on?? Seems foolish doesn't it??? SURELY by now you've got the message. I AGREE THAT WIDE TYRES ARE BETTER IN MANY CASES. I am stating that a narrower tyre produces more LONGITUDINAL traction, and a wider tyre produces more LATERAL grip. A car needs both, so it's a balancing act. (as is ALL aspects of chassis set-up).

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
It started of as you saying he`d be better of with narrow tyres.
Even tho his car handles like an upside down shopping trolley wider tyres are gonna help his cause because he`s only interested in Bars of PSI and power anyway.
<HR></BLOCKQUOTE></B>

AGAIN!!! I mentioned that narrower tyres produce more logitudinal traction ONLY because he was talking about "getting the power down" and because he meantioned about getting wider arches, so I assumed he meant he would go for wider tyres.

I can't remember having SUCH a frustrating conversation about ANYTHING.

Can anyone else, PLEASE tell me if I'm making myself clear, as I have said the same thing OVER AND OVER again and it doesn't seem to be getting through, and it may well be that I'm just not explaining myself properly?

regards

Simon

[This message has been edited by Simon de Banke (edited 12 July 2001).]

ARRON BIRD

Simon jump down of that mighty high horse your on mate.
I just caught myself the biggest fish in the sea.
Better get my tackle sorted for the next session
Seems a change of bait might be in order now as I`ve used this one up
PS I still think your talking bo11ox